1. Field of the Invention
The present invention relates to an ink composition and an ink cartridge including the ink composition. More specifically, the present invention relates to an ink composition, which exhibits low foaming properties in order to flow smoothly and has a good initial discharge capacity and less ink bleeding so that it is possible to achieve a high print quality during printing. The invention is directed to an ink cartridge including the ink composition.
2. Description of the Related Art
An ink composition is used in order that a specific object is colored with a desired color and specifically, for forming images on paper. The ink composition is produced by dissolving a colorant in a solvent. There are various types of ink composition according to the materials or methods used in preparing the ink composition, such as an ink composition prepared by dissolving dyes in an aqueous or nonaqueous medium, an ink composition prepared by dispersing pigments in an aqueous or nonaqueous medium, or a solid ink composition capable of being melted by applying heat.
Among these, ink compositions prepared by dissolving dyes in an aqueous medium are the most commonly used at present. This type of ink composition has excellent color tone and high safety when applied to the human body and the environment. This ink composition is used, for example, in a wet-type image forming apparatus capable of easily printing in the home or office where the wet-type image forming apparatus has been widely utilized in recent years. Accordingly, it is possible to form images of a high quality similar to the quality of a silver gelatin photograph.
The ink composition may be used in a wet-type image forming apparatus. To perform high-quality image recording over a long period using an aqueous ink composition for forming images, the ink composition should have suitable viscosity, surface tension, density, or other properties.
If an inlet to the nozzle, which is the discharge port of the ink composition of a wet-type image forming apparatus, becomes clogged by used ink composition, if a precipitate is produced by heat or the like, or if the properties of the ink change during the storage of the ink composition, the quality of the image formed using the ink composition naturally deteriorates.
When the ink composition is stored for a long time in an ink storage part capable of storing a large amount of the ink composition, bubbles may be formed or dissolved in the ink composition. If the ink composition is used in this state, problems arise. In other words, since the fluidity of the storage part or the flow passage of the ink composition is inhibited, or bubbles are absorbed into a nozzle with a narrow diameter when the ink composition is ejected, it may be difficult to eject the ink composition.
Furthermore, when printing at a high speed, that is, under high frequency operating conditions, the discharge capacity of the ink composition is greatly affected by fine bubbles generated in the vicinity of the heater of the heat head, or at the tip of the nozzles and adhered to the sides of the nozzles. This effect has been increasingly discussed, because characteristics necessary for high-speed printing are important factors being demanded for the ink composition.
Therefore, it is necessary to remove the bubbles contained in the ink composition, or prevent the generation of bubbles.
Accordingly, in Japanese Patent No. 3,078,184, a method of adding a fluorine- or silicone-based polymer to the ink composition is used, in order to increase the defoaming property. However, these polymers have a low solubility in the ink composition so that a simple melting method cannot be used and a dispersing operation is performed, or there is a need to use a specific solvent having a high solubility of the polymers.
Since polymer additives and a solvent with a high solubility for the additives have insufficient miscibility with other additives forming the ink composition, there are disadvantages in that layer separation and solidification easily arise in the ink composition. Due to these disadvantages, the nozzle of the print head became clogged, which generated further problems.
U.S. Pat. No. 4,957,553 discloses that secondary alkyl alcohols having 7 or fewer carbon atoms or ethylene oxide adducts thereof, acetylene alcohol or acetylene glycol are added as a defoaming agent to the ink composition, in order to prevent ink bleeding on the paper and improve the print quality while maintaining the discharge stability of the ink composition under high frequency operating conditions.
However, the defoaming performance of the defoaming agent in the ink composition disclosed in this patent, is inadequate and phenomena arise in which the ink composition is non-uniformly spread along the fibers of the paper and the edges of the formed images are frequently feathered.
Generally, it is required that the ink composition for a wet-type image forming apparatus prevent ink bleeding on regular paper and have excellent initial discharge capacity in the flow passage of the head. Recently, the head of the wet-type image forming apparatus has been reduced in size, and a narrow and complicated flow passage is formed therein. For this reason, since there are many possibilities for bubbles to remain in a bend or gap in the flow passage, it may be difficult for the ink composition to flow through the flow passage smoothly.
To enhance the initial discharge capacity of the ink composition, a method is known in which an appropriate amount of a surfactant is added to the ink composition, and surface tension is decreased to an optimum value in order to enhance the moisture level on an inside wall of the flow passage of the ink composition of the head. However, a problem with this method is that surface tension of the ink composition decreases, and simultaneously the moisture level of the paper increases to allow the ink composition to be feathered at the edge of the formed images. In other words, it is difficult in a conventional ink composition to achieve both enhancement of the initial discharge capacity and prevention of ink bleeding on the image.
Therefore, a method is required in which miscibility with other additives is guaranteed, the ink bleeding on the image is not induced while retaining the initial discharge capacity of the ink composition, the generation of bubbles in the ink composition is inhibited, and the generated bubbles are removed.